Ortataxel (1) is an antitumor compound particularly active against breast, lung, ovary, colon, prostate, kidney and pancreas tumors, even in case of resistance to known antitumor agents such as adriamycin, vinblastine and some platinum derivatives.

Ortataxel can be prepared according to the methods described in U.S. Pat. No. 7,232,916, in U.S. Pat. No. 6,737,534 and in U.S. Pat. No. 6,906,101. These patents disclose in the examples a final purification step consisting of crystallization from a mixture of acetone and hexane, which gives Ortataxel in the form of a solvate with an acetone content ranging from 4.5 to 6.5%.
The XRPD of the acetone solvate shows distinctive peaks at approximately 7.9, 9.8, 10.6, 10.9, 14.6, 16.9, 19.7, 21.3 deg 2-theta. The DSC curve shows an endothermic peak with onset at about 164° C. due to melting and release of the crystallization solvent (confirmed by a weight loss of about 5.0% in TG/DTA) and a weak exothermic peak with maximum at about 212° C. followed by an intense endothermic peak with maximum at about 247° C. due to melting and incipient decomposition. The IR shows characteristic absorption frequencies at 3521, 3321, 2971, 2953, 1826, 1762, 1706, 1526, 1366, 1238, 1165, 1072, 723 cm−1.
It is well known that volatile impurities in active pharmaceutical ingredients must comply with ICH (International Conference on Harmonisation) guidelines (Q3C); in this specific case an acetone content from 4.5 to 6.5% would not be allowed. Thus, it would be desirable to find a stable crystalline form of Ortataxel which does not contain residual solvents in amounts unacceptable from a regulatory point of view. Such crystalline form should also be chemically and thermodynamically stable, i.e. it should keep the same quality during storage, and should be obtainable through a reproducible method.